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United States Patent |
6,200,340
|
Campbell
|
March 13, 2001
|
Tilting disk heart valve having cavitation reducing contact geometry
Abstract
A heart valve prosthesis includes a valve housing having an opening formed
therein having an inmost arcuate surface and a leaflet pivotally mounted
in the opening for movement between an open position and a closed position
with the inmost arcuate surface. The leaflet has an outmost edge providing
multiple points of contact with the housing. The leaflet also forms a
leakage gap adjacent the leaflet major radius and between the inmost and
outmost surfaces such that the multiple points of contact are displaced
from the leaflet major radius and are adjacent to and on opposite sides of
the leakage gap. One or several such leaflets may be provided in the
housing. Each leaflet respectively includes the leakage gap and the
adjacent multiple points of contact.
Inventors:
|
Campbell; Louis A. (Austin, TX)
|
Assignee:
|
Sulzer Carbomedics Inc. (Austin, TX)
|
Appl. No.:
|
284000 |
Filed:
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April 1, 1999 |
Current U.S. Class: |
623/2.33 |
Intern'l Class: |
A61F 002/24 |
Field of Search: |
623/2.2,2.22,2.33,2.35
|
References Cited
U.S. Patent Documents
3476143 | Nov., 1969 | Kaster | 137/527.
|
3698018 | Oct., 1972 | Shiley | 3/1.
|
3725961 | Apr., 1973 | Magovern et al. | 3/1.
|
4276658 | Jul., 1981 | Hanson et al. | 3/1.
|
4443894 | Apr., 1984 | Klawitter | 3/1.
|
4689046 | Aug., 1987 | Bokros | 623/2.
|
4846830 | Jul., 1989 | Knoch.
| |
5147390 | Sep., 1992 | Campbell | 623/2.
|
5171263 | Dec., 1992 | Boyer | 623/2.
|
5824062 | Oct., 1998 | Patke et al. | 623/2.
|
Primary Examiner: Milano; Michael J.
Attorney, Agent or Firm: Scott; Timothy L., Lyren; Philip S.
Claims
What is claimed is:
1. A heart valve prosthesis comprising:
a valve housing having an opening formed therein, an inlet, an outlet, and
an inmost arcuate surface having a first curvature and a generally tubular
shape extending from the inlet to the outlet;
a leaflet pivotally coupled to said valve housing for movement between an
open position and a closed position, said leaflet having an upstream
surface, a downstream surface, and a peripheral edge comprising a second
curvature, different from the first curvature, wherein in said closed
position the peripheral edge of the leaflet engages the inmost arcuate
surface of the valve housing at multiple points of contact, and provides a
leakage gap between the inmost arcuate surface and the peripheral edge of
the leaflet.
2. The heart valve prosthesis of claim 1 wherein said leakage gap has a
width of between about 0.001 and 0.008 inches.
3. The heart valve as defined in claim 1 wherein the leaflet includes a
major radius, the leakage gap being adjacent the major radius.
4. A pivoting leaflet heart valve prosthesis comprising:
a valve housing having an opening formed therein, an inlet, an outlet, and
an inmost arcuate surface extending from the inlet to the outlet;
a leaflet pivotally coupled to said valve housing for movement between an
open position and a closed position, said leaflet having an upstream
surface, a downstream surface, and a peripheral edge, wherein in said
closed position the peripheral edge of the leaflet engages the inmost
arcuate surface of the valve housing at multiple points of contact between
the peripheral edge and the inmost arcuate surface, the multiple points of
contact providing a leakage gap having a width of from about 0.001 to
about 0.008 inches between said peripheral edge and said inmost arcuate
surface.
5. The heart valve as defined in claim 4 wherein the leaflet includes a
major radius adjacent the leakage gap.
6. The heart valve as defined in claim 4 wherein the multiple points of
contact engage the inmost arcuate surface between the inlet and the outlet
and displaced from the major radius.
7. A method of providing leaflet closure in a heart valve prosthesis
comprising the steps of:
providing a valve housing having an opening formed therein including an
inlet, an outlet, and an inmost arcuate surface;
providing a leaflet having an upstream surface, a downstream surface, and a
peripheral edge;
providing multiple points of contact between the peripheral edge and the
inmost arcuate surface;
providing a leakage gap at the peripheral edge separating the multiple
points of contact; and
coupling the leaflet to the valve housing for movement between an open
position and a closed position, such that when the peripheral edge engages
the inmust surface to provide the multiple points of contact in the closed
position, the leakage gap is maintained between the peripheral edge and
the inmost arcuate surface.
8. The method as defined in claim 7 wherein the step of forming includes
the step of providing a major radius on the leaflet.
9. The method of claim 7, wherein the leakage gap has a width of from about
0.001 to about 0.008 inches.
10. The method as defined in claim 9 wherein the step of mounting the
leaflet includes the step of engaging the inmost arcuate surface between
the inlet and outlet.
Description
BACKGROUND
The disclosures herein relate generally to a heart valve prosthesis
particularly to a tilting disc valve having one or more leaflets.
Tilting disk valves have an advantage over translating disk valves in that
the side profile of a tilting disk or leaflet is thin and unobstructive
when rotated to the open position compared to the translating disk or ball
type valve. The minimally obstructed passage of blood through an open
tilting leaflet valve reduces the amount of work required by the human
heart employing such a valve.
An example of a translating disk valve is disclosed in U.S. Pat. No.
3,725,961 wherein a prosthetic heart valve is disclosed having a support
ring which carries means for retaining a movable closure element in
positions adjacent one side of the ring. The support ring has a fabric
wrapping which defines, as a suturing element, an annular protrusion of
fabric of double thickness extending from the side of the ring which is
opposite the side adjacent the closure element.
U.S. Pat. No. 3,476,143 discloses a one-way mechanical heart valve
comprising a base having a passage allowing liquid to flow through the
valve. A disc located within the passage pivots about a chordal axis to an
open position and a closed position relative to a seat on the inside of
the base. In one form the seat includes an inclined upper arcuate seat and
an inclined lower arcuate seat circumventing the passage. In another form,
the seat is an annular portion of the internal annular wall which is
engaged by the periphery of the disc. Two pairs of circumferentially
spaced pivot projections provide for the pivoting of the disc about a
cordial axis of the disc. Retaining means in the form of curved side ears
or a center strut hold the disc in assembled relation with the base.
U.S. Pat. No. 3,698,018 discloses a heart valve prosthesis having a discoid
poppet mounted therein for pivotal movement between a closed and opened
position. The poppet is supported for movement by opposed, spaced support
struts which form an eccentric pivot point for opening of the valve and a
changing pivot point for closing of the valve. The spacing between the
struts is sufficient to enable rotational movement of the poppet during
operation.
U.S. Pat. No. 4,276,658 discloses a heart valve prosthesis coated in its
entirety with pyrolytic carbon. The prosthesis is formed of a base having
a blood passageway and dual leaflets pivotally secured to the base to
regulate the flow of blood through the passageway. The pivot connection
between the base and leaflets is formed by recesses in the base and
projections on the leaflets, the recesses and projection termini being
formed as surfaces of revolution. The valve is assembled by elastically
deforming the base to allow insertion of the projections within the
recesses.
U.S. Pat. No. 4,443,894 discloses a heart valve having a pair of leaflets
which are supported by respective floating pivots. The pivots guide the
leaflets between open and closed positions due to the leaflets being
pivotally mounted in dog-leg shaped depressions. The depressions each have
a downstream section which angles outward from a centerline plane of the
valve body and a connected vertical upstream section. In the closed
position, the guides reside in intermediate portions of the depressions to
unload wear forces between the guides and the depression walls for
reducing wear on the pivot points.
U.S. Pat. No. 4,689,046 discloses a heart valve prosthesis with an annular
body portion and at least one valve leaflet moveable between open, closed,
and intermediate positions. The body includes leaflet ear support
formations, each with a contoured recess having spaced apart convex ear
support surfaces. Each valve leaflet includes mounting ears with upper and
lower support surfaces of generally trapezoidal outline, a generally flat
end face portion, and two spaced apart guide surface portions tapered so
as to lie in closely spaced apart relation to the tapered guide walls in
the recess.
U.S. Pat. No. 5,147,390 discloses a bi-leaflet heart valve having an
annular body and a pair of leaflets. The leaflets pivot around improved
ears, whose motion is constrained by generally triangular recesses. The
triangular recesses have a pivotal vertex in proximity to a centerline of
the annular base and on the upstream side of the heart valve. Opposite the
pivotal vertex is a slightly convex base. The opening angle of the
leaflets can be adjusted by varying the inclination of a wall of the
triangular recess adjacent the center line. The opening angle should be
adjusted, according to the teachings of the present invention, to minimize
energy loss for a particular inside diameter of the heart valve. The
optimum opening angle can be determined by in vitro testing using an
adjustable valve and a pulse duplicator.
U.S. Pat. No. 5,824,062 discloses a bi-leaflet heart valve including an
annular base and pivoting leaflets. Each leaflet is "free-floating" within
recesses without fixed rotational axes, to increase translational movement
and redistribute stresses. Each recess fluidly communicates with a groove
extending at least partially around the inner surface of the annular base
and flow is directed through the recesses at different angles during
antegrade circulation, retrograde circulation, and valve closure. A recess
entrance angle to each of the recesses is preferably less than about
35.degree., and the pivoting mechanism within the recess includes first
and second fulcrum edges of each leaflet shiftably engaged with side
surfaces of the respective recess. The leaflets have a beveled bottom
surface having two separate planar surfaces which lie at an angle to one
another. A central region of each leaflet is spaced apart from the annular
base when the leaflet is in a fully closed position to minimize
cavitation.
As it is well known, tilting leaflet heart valves operate in a rotational
motion. These valves may include one leaflet, two leaflets (bi-leaflet) or
possibly three leaflets. The leaflet rotates about an axis displaced from
the centerline of the valve housing. When the leaflet rotates to a closed
position in the housing, the contact between the leaflet and the housing
usually occurs at a single point. As illustrated in the references above,
some valves have a simple point contact along the housing wall and others
have an overlapping surface contact.
The leaflets can fail due to cavitation. This occurs because the leaflet
moves at a very high velocity as blood is pumped through the valve. The
blood adjacent the valve closure point wants to continue to move after
valve closure occurs. Thus, a low pressure region is created adjacent the
valve contact point. If the low pressure region reaches a minus 760 mm Hg,
i.e. 1 atmosphere, cavitation occurs creating a bubble in the blood which
subsequently implodes causing cavitation erosion of any adjacent surface
such as a surface of the valve. Factors involved with cavitation include
the velocity of the moving leaflet and the valve contact geometry.
From a performance standpoint, it is desirable to have a valve which closes
quickly to reduce the quantity of blood flowing in the retrograde
direction. This is dependent on the velocity factor. The single point of
contact between the leaflet and the valve housing occurs at the farthest
distance from the axis of rotation of the leaflet. Therefore, the point of
contact had the highest linear velocity of any point on the leaflet, thus
increasing the likelihood of cavitation. The single point of contact is
near the center of the peripheral edge of the leaflet, i.e. the leaflet
major radius (MR).
Cavitation erosion occurs near the MR on the inflow side of the leaflet and
at an adjacent location on the housing. The faster the leaflet is moving
just before impact, the higher the rate of deceleration. When the leaflet
decelerates too quickly, the inertia of the blood causes it to separate
from the surface of the leaflet resulting in the above-described low
pressure region and causing the bubble to form. Thus, the cavitation
erosion damage occurs in a location which is downstream (during reverse
flow) of the leaflet/housing orifice contact upon closure.
Therefore, in view of the limitations of past developments, what is needed
is a tilting leaflet valve which moves the contact point away from the MR
without an unacceptable increase in the amount of the leakage during valve
closure.
SUMMARY
One embodiment, accordingly, provides a tilting leaflet valve with one or
more leaflets wherein there is no contact between the leaflet and the
housing at the center of the MR. To this end, a heart valve includes a
valve housing having an opening having an inmost tubular surface of a
first curvature. A pivotal leaflet is mounted in the valve for movement
between an open position and a closed position with the housing. The
leaflet has a second curvature providing multiple points of contact
between a peripheral edge of the leaflet and the inmost tubular surface of
the valve housing.
A principal advantage of this embodiment is that a leakage gap is provided
at the center of the MR thus reducing cavitation erosion. The gap is
between multiple points of contact between a peripheral edge of the
leaflet and the housing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view illustrating an embodiment of a heart
valve prosthesis taken along line 1--1 of FIG. 2.
FIG. 2 is a view illustrating an embodiment of a heart valve prosthesis as
viewed at the downstream face or outlet.
FIG. 3 is a view illustrating an embodiment of a prior art heart valve
prosthesis.
DETAILED DESCRIPTION
A heart valve prosthesis is generally designated 10, FIG. 1 and includes a
valve housing 12 having an outer arcuate brim 14, an inmost arcuate
surface 16 of a generally tubular shape, an inlet 18 and an outlet 20.
Arcuate surface 16 extends from inlet 18 to outlet 20. Housing 12 is
preferably formed of polyester knit cloth material, and inmost arcuate
surface 16 is preferably formed of pyrolytic carbon material. At least one
leaflet 22a is pivotally mounted at 24 in housing 12 for pivoting between
an open position O and a closed position C. Preferably a pair of leaflets
22a and 22b are mounted in housing 12 for pivoting outward to open
position O, and pivoting inward to the closed position C. In some
instances, a single disk or tri-leaflet valve may be provided.
Each leaflet 22a and 22b is preferably formed of pyrolytic carbon coating
over a graphite leaflet substrate material, and includes an upstream
surface 25, a downstream surface 26 and a peripheral edge 28. Arcuate
surface 16, FIG. 2, includes a first curvature R.sub.1 and peripheral edge
28 includes a second curvature R.sub.2 which is which is sufficiently
different from curvature R.sub.1 so that peripheral edge 28 engages
arcuate surface 16 only at multiple points of contact P.sub.1 and P.sub.2
when the leaflet 22a is in closed position C. As a result, a leakage gap G
is formed by a spaces defined between peripheral edge 28 and arcuate
surface 16 and is between, or separates, the multiple points of contact
P.sub.1 and P.sub.2 The gap G is adjacent a leaflet major radius
designated MR and the width of the gap G is preferably in the range of
from about 0.001 inches to about 0.008 inches.
Fluid flow is directed though valve 10 in the direction of a directional
arrow designated F, from the inlet 18 to the outlet 20. Fluid impinges on
the upstream surface 25 of each leaflet 22a and 22b and pivots the leaflet
to open position O. Due to the pumping action of the heart, leaflets 22a
and 22b rotate quickly back to the closed position C in response to fluid
flow in the retrograde direction, i.e. back toward the inlet 18 in the
direction of a directional arrow designated RG. Upon closure, each leaflet
contacts the arcuate surface 16 at the multiple contact points P.sub.1 and
P.sub.2, FIG. 2. The point contact does not occur at a single point, i.e.
the leaflet major radius MR, where the highest linear velocity of each
leaflet 22a and 22b, and thus, a higher rate of deceleration occurs. As a
result, cavitation erosion damage is minimized because the contact points
P.sub.1 and P.sub.2 are removed from the leaflet major radius MR and the
adjacent curved surfaces, i.e. arcuate surface 16 and peripheral edge 28,
define an acceptable increase in the amount of leakage at the leakage gap
G during valve closure.
This is in substantial contrast to current valves, FIG. 3, wherein the
curvatures R.sub.1 and R.sub.2 are substantially the same so that contact
between a housing 112 and a leaflet 122 occurs at the major radius MR
where the highest linear velocity of leaflet 122 also occurs in response
to fluid flow in the retrograde direction, thus maximizing cavitation
erosion damage.
As a result, one embodiment provides a heart valve prosthesis 10 including
a housing 12 having an opening formed therein which has an inmost tubular
surface 16 of a first curvature R.sub.1. A leaflet 22a is pivotally
mounted in the opening for movement between an open position O and a
closed position C with the housing 12. The leaflet 22a has a peripheral
edge 28 including a second curvature R.sub.2 which is different from the
first curvature R.sub.1. This provides multiple points of contact P.sub.1
and P.sub.2 between the peripheral edge 28 of the leaflet 22a and the
inmost tubular surface 16 of the valve housing 12.
Another embodiment provides a pivoting leaflet heart valve prosthesis 10
including a valve housing 12 having an opening formed therein which has an
inmost arcuate surface 16. A leaflet 22a is pivotally mounted in the
opening for movement between an open position O and a closed position C
with the inmost arcuate surface 16. The leaflet 22a includes a peripheral
edge 28 providing multiple points of contact P.sub.1 and P.sub.2 between
the peripheral edge and the inmost arcuate surface 16. The multiple points
of contact P.sub.1 and P.sub.2 provide a leakage gap G therebetween.
Another embodiment provides a multi-leaflet heart valve prosthesis 10
including a valve housing 12 having an opening formed therein and an
inmost arcuate surface 16. A plurality of leaflets 22a and 22b are
pivotally mounted in the opening for movement between an open position O
and a closed position C with the inmost arcuate surface 16. Each leaflet
22a and 22b has an outmost edge 28 providing multiple points of contact
P.sub.1 and P.sub.2 with the inmost arcuate surface 16. Each leaflet 22a
and 22b forms a leakage gap G between the outmost edge 28 and the inmost
arcuate surface 16. The leakage gap G is between the multiple points of
contact P.sub.1 and P.sub.2.
A further embodiment provides a method of providing leaflet closure in a
heart valve prosthesis 10 by providing a valve housing 12 having an
opening formed therein including an inmost arcuate surface 16. A leaflet
22a has a peripheral edge 28. Multiple points of contact P.sub.1 and
P.sub.2 are provided between the peripheral edge 28 and the inmost arcuate
surface 16. A leakage gap G is provided at the peripheral edge 28
separating the multiple points of contact P.sub.1 and P.sub.2. The leaflet
22a is mounted in the valve 10 for pivotal movement between an open
position O and a closed position C so that when the multiple points of
contact P.sub.1 and P.sub.2 engage the inmost arcuate surface 16 in the
closed position C, the leakage gap G is maintained between the peripheral
edge 28 and the inmost arcuate surface 16.
As it can be seen, the principal advantages of these embodiments are that
in a tilting disk heart valve with one or more occluders, there is no
contact between the leaflet major radius MR and the gap G near the center
of the major radius MR. The leakage gap G is provided at the center of the
major radius MR thus reducing cavitation erosion. The gap is between
multiple points P.sub.1 and P.sub.2 of contact between a peripheral edge
of the leaflet and the housing.
Although illustrative embodiments have been shown and described, a wide
range of modification, change and substitution is contemplated in the
foregoing disclosure and in some instances, some features of the
embodiments may be employed without a corresponding use of other features.
Accordingly, it is appropriate that the appended claims be construed
broadly and in a manner consistent with the scope of the embodiments
disclosed herein.
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